Catalyst system for uretdione dispersions

ABSTRACT

The present invention relates to a catalyst system comprising: A) at least one compound selected from azoles, oxazoles, thiazoles, benzotriazole, benzimidazole, benzoxazole and salts thereof; B) at least one acid catcher, which contains at least one epoxy group; and C) at least one catalyst containing an N,N,N′-trisubstituted amidine structure with an amidine group content of from 12.0 to 47.0 wt %, calculated as CN2 with molecular weight=40. The invention also relates to a kit which comprises the catalyst system of the present invention and an aqueous uretdione dispersion having an acid number of from 1 to 100 KOH/g and additionally at least one carboxyl group. The invention further relates to a method for producing a polyurethane layer using the catalyst system of the present invention and said uretdione dispersion, and to the obtained polyurethane layer, and to the use of the catalyst system for curing aqueous acidic uretdione dispersions and/or for the production of paints or coatings.

The present invention relates to a catalyst system comprising

-   A) at least one compound selected from azoles, oxazoles, thiazoles,     benzotriazole, benzimidazole, benzoxazole, and salts thereof; -   B) at least one acid scavenger containing at least one epoxy group;     and -   C) at least one catalyst containing an N,N,N′-trisubstituted amidine     structure and having an amidine group content of 12.0 to 47.0% by     weight calculated as CN2 with molecular weight=40. The present     invention further relates to a kit that comprises the catalyst     system of the present invention and an aqueous uretdione dispersion     that has an acid value of 1 to 100 mg KOH/g and also at least one     carboxyl group, to a process for producing a polyurethane layer with     the catalyst system of the present invention and for producing said     uretdione dispersion and the resulting polyurethane layer, and also     to the use of the catalyst system for curing aqueous acidic     uretdione dispersions and/or for producing paints or coatings.

The production of polyurethane layers based on uretdione dispersions is known. This is done primarily by using uretdione group-containing powder coating compositions.

EP 0 803 524 A1 describes amidines as catalysts in uretdione group-containing PUR powder coating compositions. The uretdione component and the OH-containing binder component are solids at room temperature. These are applied to the substrate by electrostatic powder spraying or fluidized-bed sintering, with the curing temperature being above 130° C. The use thereof as aqueous systems is not possible.

EP1526146 A1 likewise describes a polyurethane powder coating composition. It is disclosed in this regard that the activity of the amidine catalysts decreases significantly in the presence of acids. Uretdione group-containing polyaddition compounds terminating in epoxy groups and having a melting point of 40-130° C. are used. The epoxide is anchored in the backbone in these compounds, for example using 2,3-epoxy-1-propanol and/or epoxidized soybean oil. In addition, a catalyst from the group consisting of metal acetylacetonates, metal hydroxides, metal alkoxides, quaternary ammonium hydroxides, quaternary ammonium fluorides or quaternary ammonium carboxylates is used for curing. The curing temperature for this is usually 120-160° C. The use thereof as aqueous systems is not possible.

WO 2009/095117 A1 describes powder coating compositions that have a melting point of more than 40° C. Quaternary ammonium salts or phosphonium salts are used as catalysts. An epoxy compound composed of terephthalic acid diglycidyl ether and trimellitic acid triglycidyl ether (Araldite PT 912) or acetylacetonate is used as cocatalyst. Curing temperatures below 120° C. are not possible with these systems. The use thereof as aqueous systems is likewise not possible.

However, the application of powder coating compositions to produce polyurethane layers is complex in terms of the devices required for this. It is moreover desirable to use lower crosslinking temperatures in order to make the process more energy-efficient. The starting point should therefore take the form of aqueous polyurethane dispersions that contain uretdione groups and are easier and therefore more advantageous to handle. Dispersions that are non-ionically hydrophilized exhibit permanent hydrophilicity and poor resistance to chemicals and water. Ionically hydrophilized dispersions should therefore be used. Anionic dispersions are known to be better than cationic dispersions. Customary anionic systems contain carboxyl groups to provide better dispersion. Catalysts such as sodium triazolate that are sensitive to acids, i.e. including to carboxyl groups, consequently appeared unsuitable.

An acidic, i.e. anionic, self-crosslinking polyuretdione dispersion is disclosed in, for example, DE 10 2005 036 654 A1. The crosslinking temperatures of such systems are, however, above 130° C.

A catalyst system was therefore required that is tolerant to acids and results in at least equally good crosslinking. These polyurethane dispersions were not, however, crosslinkable with the catalysts known from the prior art, for example the catalysts disclosed in U.S. Pat. No. 9,080,074.

The object of the present invention was therefore to develop catalyst systems for crosslinking aqueous anionic polyurethane dispersions that contain uretdione groups. The polymers are to be crosslinkable via the uretdione groups. It is to be possible for the polymerization to be able to take place preferably below 100° C. (low-temperature crosslinking). The catalyst systems are also to be nonsensitive to acidic conditions. Preferably, the catalyst systems are not to contain any organometallic compounds.

Surprisingly, it has been possible to find catalyst systems that are suitable for crosslinking aqueous compositions containing acidic groups and in particular uretdione groups and with which crosslinking temperatures below 100° C. are achieved.

The object of the present invention was achieved by:

A catalyst system comprising or consisting of

-   A) at least one compound selected from azoles, oxazoles, thiazoles,     benzotriazole, benzimidazole, benzoxazole, and salts thereof; -   B) at least one acid scavenger containing at least one epoxy group;     and -   C) at least one catalyst containing an N,N,N′-trisubstituted amidine     structure and having an amidine group content of 12.0 to 47.0% by     weight calculated as CN2; molecular weight=40.

In particular, the present invention relates to:

-   1. A catalyst system comprising or consisting of     -   A) at least one compound selected from azoles, oxazoles,         thiazoles, benzotriazole, benzimidazole, benzoxazole, and salts         thereof;     -   B) at least one acid scavenger containing at least one epoxy         group; and     -   C) at least one catalyst containing an N,N,N′-trisubstituted         amidine structure and having an amidine group content of 12.0 to         47.0% by weight calculated as CN2, molecular weight=40. -   2. The catalyst system according to embodiment 1, characterized in     that the at least one compound A) is selected from pyrazole,     imidazole, 1,2,3-triazole, 1,2,4-triazole, benzotriazole and salts     thereof; in particular from 1,2,3-triazole, 1,2,4-triazole,     benzotriazole, and salts thereof, more preferably from the alkali     metal and alkaline earth metal salts of 1,2,3-triazole,     1,2,4-triazole, and benzotriazole; most preferably from the Na, Li,     and K salts of 1,2,3-triazole, 1,2,4-triazole, and benzotriazole. -   3. The catalyst system according to embodiment 1 or 2, characterized     in that the at least one acid scavenger B) is selected from     aliphatic or aromatic alcohols, diols, polyols, ethers and acids     containing at least one epoxy group. -   4. The catalyst system according to any of the preceding     embodiments, characterized in that the at least one catalyst     containing an N,N,N′-trisubstituted amidine structure and having an     amidine group content of 12.0 to 47.0% by weight calculated as CN2,     molecular weight=40, C) is selected from optionally substituted     amidine bases bearing alkyl, aralkyl or allyl radicals, wherein the     CN double bond of the amidine structure is both part of an     open-chain molecule and an element of a cyclic or bicyclic system,     or else may be positioned exocyclically on a ring system, or any     desired mixtures of such amidines. -   5. The catalyst system according to any of the preceding     embodiments, characterized in that A) and B) are present in a mass     ratio of 1:1 to 10:1, preferably 2:1 to 6:1, and/or A) and C) are     present in a mass ratio of 0.5:1 to 5:1, preferably 1:1 to 2:1,     and/or B) and C) are present in a mass ratio of 1:1 to 1:10,     preferably 1:1 to 1:6. -   6. A kit comprising the catalyst system according to any of     embodiments 1 to 5 and, separately from this, an aqueous uretdione     dispersion characterized in that it has an acid value of 1 to 100 mg     KOH/g, preferably 2 to 50 mg KOH/g, more preferably 5 to 30 mg     KOH/g, preferably measured according to DIN EN ISO 2114: 2002-06     with acetone and ethanol in a weight ratio of 2:1 as solvent, and     also has at least one carboxyl group. -   7. The kit according to embodiment 6, characterized in that the     equivalents ratio of uretdione to hydroxy groups used is 0.5:1 to     1:0.5, preferably 0.75:1 to 1:0.75, most preferably 1:1. -   8. A process for producing a polyurethane layer comprising the steps     of     -   i) providing an aqueous uretdione dispersion having an acid         value of 1 to 100 mg KOH/g, preferably 2 to 50 mg KOH/g, more         preferably 5 to 30 mg KOH/g, preferably measured according to         DIN EN ISO 2114: 2002-06 with acetone and ethanol in a weight         ratio of 2:1 as solvent, and having at least one carboxyl group;

ii) adding the catalyst system according to any of embodiments 1 to 5, preferably with stirring;

-   -   iii) applying the mixture obtained in ii) to a substrate;     -   iv) drying the mixture from step iii), preferably at room         temperature, and     -   v) curing the mixture from step iv) by heating to 120° C.,         preferably to 100° C., for up to 180 minutes, preferably up to         120 minutes.

-   9. The polyurethane layer, in particular polyurethane film,     obtainable by a process according to embodiment 8.

-   10. The use of the catalyst system according to any of embodiments 1     to 5 for curing aqueous uretdione dispersions having an acid value     of 1 to 100 mg KOH/g, preferably 2 to 50 mg KOH/g, more preferably 5     to 30 mg KOH/g, preferably measured according to DIN EN ISO 2114:     2002-06 with acetone and ethanol in a weight ratio of 2:1 as     solvent, and having at least one carboxyl group, and/or for     producing paints or coatings, in particular polyurethane films.

Unless explicitly stated otherwise, molecular weights in the present invention are determined by GPC (gel-permeation chromatography) using polystyrene standards.

Unless explicitly stated otherwise, % by weight in the present invention refers to the total weight of the respective system or the total weight of the respective component. For example, a copolymer may have a content of a particular monomer that is expressed in % by weight, in which case the percent by weight values would be based on the total weight of the copolymer.

Unless explicitly stated otherwise, the expression “at least one” refers to the type of compound and not to individual molecules. For example, at least one acid scavenger B) is to be understood as meaning that at least one type of acid scavenger is present, but is present in the composition in an indeterminate number of molecules. It is also thus possible for two or more types of acid scavenger to be present, each in an indeterminate number if the amounts are not defined.

A kit in the context of the present invention is a system in which the catalyst system of the present invention and the aqueous carboxyl group-containing uretdione dispersion are present spatially separately from one another.

The catalyst system comprises at least one compound A) selected from azoles, oxazoles, thiazoles, benzotriazole, benzimidazole, benzoxazole, and salts thereof. The at least one compound A) is preferably selected from pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, benzotriazole and salts thereof. The salts are preferably alkali metal, alkaline earth metal or ammonium salts. The at least one compound A) is especially preferably selected from 1,2,3-triazole, 1,2,4-triazole, benzotriazole and salts thereof; more preferably from the alkali metal and alkaline earth metal salts of 1,2,3-triazole, 1,2,4-triazole, and benzotriazole; most preferably from the Na, Li, and K salts of 1,2,3-triazole, 1,2,4-triazole, and benzotriazole, in particular the sodium salts thereof.

The catalyst system further comprises at least one acid scavenger B) that contains at least one epoxy group. In a preferred embodiment, the at least one acid scavenger B) is selected from aliphatic or aromatic alcohols, diols, polyols, ethers and acids containing at least one epoxy group, preferably selected from C₂₋₂₀ alcohols, C₂₋₂₀ diols, C₄₋₅₀ polyols having at least 3 hydroxy groups, C₃₋₅₀ ethers and polyethers and C₃₋₂₀ acids containing at least one epoxy group. Particular preference is given to monofunctional and polyfunctional glycidyl ethers, for example butyl glycidyl ether, pentaerythritol tetraglycidyl ether, glycidyl isopropyl ether, 2-ethylhexyl glycidyl ether, polyethylene glycol diglycidyl ether, 1,4-cyclohexanedimethanol diglycidyl ether or polyfunctional glycidyl ethers commercially available from Hexion under the HELOXY™ name.

The at least one acid scavenger B) preferably has a viscosity of 5 to 500 mPas, more preferably 50 to 250 mPas, most preferably 100 to 200 mPas, measured at 25° C. in accordance with DIN 53015:2001-02.

In a further preferred embodiment, the at least one acid scavenger B) has an epoxy equivalent (weight per epoxy group) of 120 to 650 g/eq, preferably 125 to 250 g/eq, measured in accordance with DIN 16945:1989-03.

The at least one acid scavenger B) likewise preferably has an epoxy value of 20.0 to 35.0%, more preferably 23.5 to 33.0%, most preferably 26.5 to 32.5%, measured in accordance with DIN 16945:1989-03.

The catalyst system further comprises at least one catalyst containing an N,N,N′-trisubstituted amidine structure and having an amidine group content of 12.0 to 47.0% by weight calculated as CN2; molecular weight=40. Examples of suitable amidine catalysts C) in which the CN double bond is part of an open-chain molecule are N,N-dimethyl-N′-phenylformamidine or N,N,N′-trimethylformamidine, the preparation of which is described, for example, in Chem. Ber. 98, 1078 (1965). Examples of suitable amidines C) in which the CN double bond is part of a cyclic system are 2-methyltetrahydropyrimidines substituted in the 1-position, as are obtainable for example according to the teaching of DE 2 439 550 A1 by reacting N-monosubstituted 1,3-propanediamines with acetoacetic acid derivatives, or monocyclic amidine bases such as those obtainable according to DE 1 078 568 A1 by reacting carbamoyl chlorides formed from secondary amines with lactams. Examples of suitable catalysts C) in which the CN double bond is positioned exocyclically on a ring system are imines of N-alkyl-substituted lactams, such as 2-methylimino-1-methylpyrrolidone, the preparation of which is described, for example, in Chem. Ber. 101, 3002 (1968).

Preference as the at least one component C) is given to bicyclic catalysts containing N,N,N′-trisubstituted amidine structures of the general formula (1)

in which m is an integer from 1 to 9, preferably from 1 to 3, and n is an integer from 1 to 3, preferably 2.

The preparation of such bicyclic amidines is known and is described, for example, in DE 1 545 855 A1 or in EP 662 476 A1. Particularly preferred catalysts C) are 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), in particular DBU.

In a preferred embodiment, no ammonium salts or phosphonium salts are present. In a further preferred embodiment, no organometallic catalysts and/or quaternary ammonium hydroxides, quaternary ammonium fluorides or quaternary ammonium carboxylates are present. In a further preferred embodiment, no further catalysts are present.

The invention further relates to a kit in which an acidic aqueous uretdione dispersion and the catalyst system of the present invention are present separately from one another. Suitable uretdione dispersions are those generally known to those skilled in the art, provided that they have an acid value of 1 to 100 mg KOH/g, preferably 2 to 50 mg KOH/g, more preferably 5 to 30 mg KOH/g, preferably measured according to DIN EN ISO 2114: 2002-06 with acetone and ethanol in a weight ratio of 2:1 as solvent, and have at least one carboxyl group.

In a preferred embodiment, the aqueous uretdione dispersion according to the present invention has an equivalents ratio of uretdione to hydroxy groups used of 0.5:1 to 1:0.5, preferably 0.75:1 to 1:0.75, most preferably 1:1.

Suitable aqueous polyurethane dispersions typically contain the essential structural units (I) and (II) in the same polymer molecule

in which R is an aliphatic, cycloaliphatic, araliphatic or aromatic radical derived from a polyisocyanate selected from the group consisting of tetramethylene diisocyanate, cyclohexane 1,3-diisocyanate or cyclohexane-1,4-diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate IPDI), dicyclohexylmethane-2,4′-diisocyanate and/or dicyclohexylmethane-4,4′-diisocyanate, tetramethylxylylene diisocyanate (TMXDI), triisocyanatononane, tolylene diisocyanate (TDI), diphenylmethane-2,4′-diisocyanate and/or diphenylmethane-4,4′-diisocyanate (MDI), triphenylmethane-4,4′-diisocyanate or naphthylene-1,5-diisocyanate, R′ is an alkyl radical, preferably ethyl or methyl, particularly preferably methyl, X is a carboxylic acid (COOH) or carboxylate (COO⁻) radical, and Y is NH₂, NHR″ or OH, preferably OH, and R″ is an alkyl radical, preferably hexyl, butyl, propyl, ethyl or methyl, particularly preferably methyl.

The dispersion that may be used in the present invention may contain uretdione groups (acting as capped isocyanates) and hydroxy groups in one molecule.

Suitable uretdione dispersions may be prepared by the process below, which comprises the following steps:

In a first step (I), an ionic uretdione group-containing, hydrophilized prepolymer containing terminal hydroxy or isocyanate groups is prepared by reacting

-   -   at least one uretdione group-containing polyisocyanate component         (A2′) having an isocyanate group functionality of ≥2 and a ratio         of uretdione to isocyanate groups of at least 0.10 and     -   at least one compound (C′) that has at least one         isocyanate-reactive and also one acid-functional group,     -   optionally a further polyol component (B1′) having a hydroxy         group functionality of ≥2 and a molecular weight M of 62 to 500         g/mol, preferably 62 to 400 g/mol, more preferably 62 to 300         g/mol,     -   optionally one or more polyisocyanates (A1′) having an NCO         functionality of ≥2 that are different than (A2′) and preferably         contain no uretdione groups,         in a second step.         (II) the uretdione group-containing prepolymer,         which may contain terminal hydroxy groups or isocyanate groups,         is converted, through reaction of     -   optionally one or more polyol components (B2) having a hydroxy         group functionality of >1 and also     -   optionally polyisocyanates (A1′) having an NCO functionality of         ≥2 and     -   at least one polyol component (B3′) having a mean hydroxy group         functionality of ≥2 and a molecular weight Mn of 500 to 5000         g/mol, preferably 500 to 3000 g/mol, more preferably 500 to 2000         g/mol, into an isocyanate-free and hydroxy-functional         polyurethane polymer, which is completely or partially         neutralized by mixing with a neutralizing agent (N) and         dispersed in water. To this aqueous composition is then added         the catalyst system of the present invention.

The first two steps in the synthesis may likewise be carried out in reverse order or else in a single reaction step. It is likewise possible to use a pro rata amount of the polyol component (B1′) in the preparation of the prepolymer (I). Similarly, it is possible likewise to use a pro rata amount of compound (C′) in the prepolymerization (II) of the uretdione group-containing polyisocyanate mixture.

In a preferred embodiment of the invention, the addition of the polyol component (B3′) may be followed, either at the same time or in a further step, by another addition of an acid-functional compound (C′) and addition of a further polyisocyanate component (A1′).

The ratio of the isocyanate groups, including the uretdione groups, to all groups that are reactive toward isocyanate groups is preferably from 0.5 to 5.0:1, more preferably from 0.6 to 2.0:1, in particular from 0.8 to 1.5:1.

Suitable polyisocyanate components (A1′) are aliphatic, cycloaliphatic, araliphatic, and/or aromatic isocyanates having a mean functionality of 2 to 5, preferably 2, and having an isocyanate content of 0.5 to 60% by weight, preferably of 3 to 40% by weight, more preferably of 5 to 30% by weight, for example tetramethylene diisocyanate, cyclohexane 1,3-diisocyanate and cyclohexane 1,4-diisocyanate, pentamethylene diisocyanate (PDI), hexamethylene diisocyanate (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate IPDI), dicyclohexylmethane 2,4′-diisocyanate and/or dicyclohexylmethane 4,4′-diisocyanate, tetramethylxylylene diisocyanate (TMXDI), triisocyanatononane, tolylene diisocyanate (TDI), diphenylmethane 2,4′-diisocyanate and/or diphenylmethane 4,4′-diisocyanate (MDI), triphenylmethane 4,4′-diisocyanate or naphthylene 1,5-diisocyanate, and any desired mixtures of such isocyanates. Preference is given to isophorone diisocyanate, dicyclohexylmethane 2,4′-diisocyanate and/or dicyclohexylmethane 4,4′-diisocyanate or hexamethylene diisocyanate, in particular isophorone diisocyanate.

Likewise suitable as polyisocyanate components (A1′) are polyisocyanates having an isocyanurate, iminooxadiazinetrione, urethane, allophanate, biuret, and/or oxadiazinetrione structure prepared through modification of the abovementioned di- and/or triisocyanates as described by way of example in J. Prakt. Chem. 336 (1994) 185-200 or DE-A 16 70 666 and EP-A 798 299.

Suitable polyisocyanates (A1′) are additionally the known prepolymers having terminal isocyanate groups, as are obtainable in particular by reacting the abovementioned simple polyisocyanates, especially diisocyanates, with substoichiometric amounts of organic compounds having at least two functional groups reactive toward isocyanates. In these known prepolymers, the ratio of isocyanate groups to hydrogen atoms reactive towards NCO is 1.05:1 to 10:1, preferably 1.5:1 to 4:1, with the hydrogen atoms preferably originating from hydroxy groups. The type and proportions of the starting materials used in the preparation of NCO prepolymers are chosen such that the NCO prepolymers preferably have a mean NCO functionality of 2 to 3 and a number average molar mass of 300 to 10 000 g/mol, preferably 800 to 4000 g/mol.

Suitable as component (A2′) are polyisocyanates containing at least one isocyanate group and at least one uretdione group. These are prepared through the reaction of suitable starting isocyanates as described, for example, in WO 02/92657 A1 or WO 2004/005364 A1. In this reaction, some of the isocyanate groups are converted into uretdione groups under catalysts, for example with triazolates or 4-dimethylaminopyridine (DMAP) as catalysts. Examples of isocyanates from which the uretdione-containing structural units (A2) are formed are tetramethylene diisocyanate, cyclohexane 1,3-diisocyanate and cyclohexane 1,4-diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate IPDI), dicyclohexylmethane 2,4′-diisocyanate and/or dicyclohexylmethane 4,4′-diisocyanate, tetramethylxylylene diisocyanate (TMXDI), triisocyanatononane, tolylene diisocyanate (TDI), diphenylmethane 2,4′-diisocyanate and/or diphenylmethane 4,4′-diisocyanate (MDI), triphenylmethane 4,4′-diisocyanate or naphthylene 1,5-diisocyanate, and any desired mixtures of such isocyanates. Preference is given to isophorone diisocyanate, dicyclohexylmethane 2,4′-diisocyanate and/or dicyclohexylmethane 4,4′-diisocyanate or hexamethylene diisocyanate.

Apart from the isocyanate groups and uretdione groups, component (A2′) may also contain isocyanurate, biuret, allophanate, urethane and/or urea structures.

The polyol component (B1′) preferably contains dihydric to hexahydric polyol components having a molecular weight Mn of 62 to 500 g/mol, preferably 62 to 400 g/mol, particularly preferably 62 to 300 g/mol. Examples of preferred polyol components (B1′) are 1,4-butanediol and/or 1,3-butanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, polyester polyols and/or polyether polyols having an average molecular weight Mn of less than or equal to 500 g/mol.

Suitable acid-functional compounds (C′) are hydroxy-functional carboxylic acids, preferably mono- and dihydroxycarboxylic acids, for example 2-hydroxyacetic acid, 3-hydroxypropanoic acid or 12-hydroxy-9-octadecanoic acid (ricinoleic acid). Preferred carboxylic acids (C′) are those in which the reactivity of the carboxyl group is hindered by steric effects, for example lactic acid. Particular preference is given to 3-hydroxy-2,2-dimethylolpropanoic acid (hydroxypivalic acid) or dimethylolpropionic acid, with most preference given to the exclusive use of dimethylolpropionic acid.

If component (B1) is used on a pro rata basis in step (I), its proportion is, however, not more than 50% by weight based on the sum of components (C′) and (B1′). Preference is given to the exclusive use of component (C′) in step (I).

The polyol component (B2′) is selected from the group consisting of

b1) dihydric to hexahydric alcohols having an average molecular weight Mn of 62 to 300 g/mol, preferably of 62 to 182 g/mol, more preferably of 62 to 118 g/mol, b2) linear difunctional polyols having an average molecular weight Mn of 350 to 4000 g/mol, preferably of 350 to 2000 g/mol, more preferably of 350 to 1000 g/mol, b3) monofunctional linear polyols having an average molecular weight Mn of 350 to 2500 g/mol, preferably of 500 to 1000 g/mol,

Suitable polyol components (b1) are dihydric to hexahydric alcohols and/or mixtures thereof having no ester groups. Typical examples are 1,2-ethanediol, 1,2-propanediol and 1,3-propanediol, 1,4-butanediol, 1,2-butanediol or 2,3-butanediol, 1,6-hexanediol, 1,4-dihydroxycyclohexane, glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, and sorbitol. Alcohols having ionic groups or groups that can be converted into ionic groups may of course also be used as component (b1). Preference is given to, for example, 1,4-butanediol or 1,3-butanediol, 1,6-hexanediol or trimethylolpropane, and mixtures thereof.

Suitable linear difunctional polyols (b2) are selected from the group consisting of polyethers, polyesters, and/or polycarbonates. The polyol component (b2) preferably comprises at least one diol containing ester groups and having a molecular weight Mn of 350 to 4000 g/mol, preferably of 350 to 2000 g/mol, more preferably of 350 to 1000 g/mol, This is the average molecular weight that is calculable from the hydroxyl value. The ester diols are generally mixtures in which individual constituents having a molecular weight below or above these limits may also be present in minor amounts. These are polyester diols known per se that are formed from diols and dicarboxylic acids.

Examples of suitable diols are 1,4-dimethylolcyclohexane, 1,4-butanediol or 1,3-butanediol, 1,6-hexanediol, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane and pentaerythritol, and mixtures of such diols. Examples of suitable dicarboxylic acids are aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid, cycloaliphatic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, and the anhydrides thereof, and aliphatic dicarboxylic acids such as succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, and sebacic acid or the anhydrides thereof, which are used with preference.

Polyester diols based on adipic acid, phthalic acid, isophthalic acid, and tetrahydrophthalic acid are preferably used as component (b2). Examples of preferred diols are 1,4-butanediol or 1,3-butanediol, 1,6-hexanediol or trimethylolpropane, and mixtures thereof.

Also suitable as component (b2) are polycaprolactone diols having an average molecular weight of 350 to 4000 g/mol, preferably of 350 to 2000 g/mol, more preferably of 350 to 1000 g/mol, that are prepared in a manner known per se starting from a diol or diol mixture of the type mentioned above by way of example as starter and 8-caprolactone. The preferred starter molecule for this is 1,6-hexanediol. Particular preference is given to polycaprolactone diols that have been prepared by polymerizing 8-caprolactone using 1,6-hexanediol as starter.

(Co)polyethers of ethylene oxide, propylene oxide, and/or tetrahydrofuran may also be used as the linear polyol component (b2). Preference is given to polyethers having an average molecular weight Mn of 500 to 2000 g/mol, for example polyethylene oxides or polytetrahydrofuran diols.

Also suitable as (b2) are hydroxy group-containing polycarbonates, preferably having an average molecular weight Mn of 400 to 4000 g/mol, preferably of 400 to 2000 g/mol, for example hexanediol polycarbonate and polyester carbonates.

Examples of suitable monofunctional linear polyethers (b3) are (co)polyethers obtained from ethylene oxide and/or propylene oxide. Preference is given to monoalcohol-started polyalkylene oxide polyethers having an average molecular weight Mn of 350 to 2500 g/mol and containing at least 70% ethylene oxide units.

Particular preference is given to (co)polymers containing more than 75% ethylene oxide units and having a molecular weight Mn of 350 to 2500 g/mol, preferably of 500 to 1000 g/mol. The starter molecules for the preparation of these polyethers are preferably monofunctional alcohols having 1 to 6 carbon atoms.

Suitable polyols (B3′) are polyols having an OH functionality greater than or equal to 2 and having an average molecular weight of 500 to 5000 g/mol, preferably of 500 to 3000 g/mol, more preferably of 500 to 2000 g/mol.

Examples of preferred polyols (B3′) are polyethers having an average molecular weight of 300 to 2000 g/mol and a mean functionality of 2.5 to 4 OH groups per molecule. Preference is likewise given to polyesters having a mean OH functionality of 2.5 to 4.0. Suitable diols and dicarboxylic acids for the polyesters are those mentioned under component (b2), but additionally include tri- to hexafunctional short-chain polyols such as trimethylolpropane, pentaerythritol or sorbitol. Preference is given to the use of polyester polyols based on adipic acid, phthalic acid, isophthalic acid, and tetrahydrophthalic acid, and also 1,4-butanediol and 1,6-hexanediol.

Likewise suitable as component (B3′) are (co)polyethers of ethylene oxide, propylene oxide, and/or tetrahydrofuran having a mean functionality greater than or equal to 2, and also polycarbonate polyols.

The process according to the invention should be carried out in such a way that the amounts of unreacted excess components (A) and/or (B1) in the reaction of components (A′) and (B1) according to the theoretical stoichiometric equation are as low as possible.

The aqueous dispersions containing the self-crosslinking polyurethanes according to the invention are prepared by prior art processes.

The carboxylic acid groups present in the polyurethanes according to the invention are preferably neutralized with suitable neutralizing agents (N) to an extent of at least 50%, more preferably 80% to 120%, particularly preferably 95 to 105%, and then dispersed with deionized water. The neutralization can take place before, during or after the dispersion or dissolution step. Neutralization before the addition of water is, however, preferred.

Examples of suitable neutralizing agents (N) are triethylamine, dimethylaminoethanol, dimethylcyclohexylamine, triethanolamine, methyldiethanolamine, diisopropanolamine, ethyldiisopropylamine, diisopropylcyclohexylamine, N-methylmorpholine, 2-amino-2-methyl-1-propanol, ammonia or other customary neutralizing agents or neutralizing mixtures thereof.

Preference is given to tertiary amines such as triethylamine and diisopropylhexylamine, and particular preference to dimethylethanolamine.

To regulate the viscosity, solvents may optionally also be added to the reaction mixture. All known paint solvents such as N-methylpyrrolidone, methoxypropyl acetate, Proglyde® DMM (Dow Chemicals), Shellsol® (Shell AG) or xylene are suitable. Preference is given to using amounts of 0 to 10% by weight, preferably 0 to 5% by weight. The solvent is preferably added during the polymerization.

Auxiliaries and additives optionally additionally used in coatings technology, for example pigments, leveling agents, or bubble-preventing additives, may likewise be added to the aqueous dispersions according to the invention.

Alternative uretdione dispersions of the present invention that are likewise suitable are storage-stable, reactive aqueous uretdione group-containing compositions that a physical mixture, dispersed in water and optionally organic solvents, of

-   (A11) at least one uretdione group-containing curing agent based on     aliphatic, (cyclo)aliphatic, araliphatic, and/or aromatic     polyisocyanates that contain no chemically bonded hydrophilizing     groups; -   B12) at least one polyol containing hydroxy groups that contains at     least one chemically bonded carboxylic acid group; -   (C13) optionally solvents, and -   (D14) optionally auxiliaries and additives,     wherein the quantitative ratio of components (A11) and (B12) is such     that the molar ratio of the NCO groups of the curing agent (A11)     present as uretdione to NCO-reactive groups of the polyol (B12) is     0.5:1 to 1:0.5 and the aqueous composition has an acid value of 1 to     100 mg KOH/g, preferably 2 to 50 mg KOH/g, more preferably 5 to 30     mg KOH/g, preferably measured in accordance with DIN EN ISO 2114:     2002-06, with acetone and ethanol in a weight ratio of 2:1 as     solvent. To this aqueous composition is then added the catalyst     system of the present invention.

Uretdione group-containing polyisocyanates that are suitable as starting compounds for component (A11) are the polyisocyanates (A2′) described above.

The conversion of these uretdione group-containing polyisocyanates into uretdione group-containing curing agents (A11) involves the reaction of the free NCO groups of the starting compounds (A2′) with the polyol component (B1′), optionally with the additional use of the polyol component (b2).

The polyol component used in the preparation of the uretdione group-containing curing agents (A11) may also take the form of diols bearing low-molecular-weight ester groups and having an average molecular weight, calculable from the functionality and hydroxyl value, of 134 to 349 g/mol, preferably 176 to 349 g/mol.

Examples of these include the diols containing ester groups that are known per se, or mixtures of such diols, as can be prepared for example by reacting alcohols with substoichiometric amounts of dicarboxylic acids, corresponding dicarboxylic anhydrides, corresponding dicarboxylic esters of lower alcohols or lactones. Examples of suitable acids are succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic acid, maleic acid, maleic anhydride, dimethyl terephthalate, and bisglycol terephthalate. Examples of suitable lactones for preparing these ester diols are β-propiolactone, γ-butyrolactone, γ- and δ-valerolactone, ε-caprolactone, 3,5,5- and 3,3,5-trimethylcaprolactone or any desired mixtures of such lactones.

Amino-functional compounds may also be used in the preparation of the uretdione group-containing curing agents (A11). Examples of suitable low-molecular-weight amino-functional compounds are aliphatic and cycloaliphatic amines and amino alcohols containing primary and/or secondary amino groups, for example cyclohexylamine, 2-methyl-1,5-pentanediamine, diethanolamine, monoethanolamine, propylamine, butylamine, dibutylamine, hexylamine, monoisopropanolamine, diisopropanolamine, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, isophoronediamine, diethylenetriamine, ethanolamine, aminoethylethanolamine, diaminocyclohexane, hexamethylenediamine, methyliminobispropylamine, iminobispropylamine, bis(aminopropyl)piperazine, aminoethylpiperazine, 1,2-diaminocyclohexane, triethylenetetramine, tetraethylenepentamine, bis(4-aminocyclohexyl)methane, bis(4-amino-3-methylcyclohexyl)methane, bis(4-amino-3,5-dimethylcyclohexyl)methane, bis(4-amino-2,3,5-trimethylcyclohexyl)methane, 1,1-bis(4-aminocyclohexyl)propane, 2,2-bis(4-aminocyclohexyl)propane, 1,1-bis(4-aminocyclohexyl)ethane, 1,1-bis(4-aminocyclohexyl)butane, 2,2-bis(4-aminocyclohexyl)butane, 1,1-bis(4-amino-3-methylcyclohexyl)ethane, 2,2-bis(4-amino-3-methylcyclohexyl)propane, 1,1-bis(4-amino-3,5-dimethylcyclohexyl)ethane, 2,2-bis(4-amino-3,5-dimethylcyclohexyl)propane, 2,2-bis(4-amino-3,5-dimethylcyclohexyl)butane, 2,4-diaminodicyclohexylmethane, 4-aminocyclohexyl-4-amino-3-methylcyclohexylmethane, 4-amino-3,5-dimethylcyclohexyl-4-amino-3-methylcyclohexylmethane, and 2-(4-aminocyclohexyl)-2-(4-amino-3-methylcyclohexyl)methane.

Solvents may optionally be used in the preparation of the uretdione group-containing curing agents (A11). Suitable solvents for the uretdione group-containing curing agents (A11) are all liquid substances that do not react with other constituents, for example acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, Solvesso 100, Solvesso 150, propylene glycol mono-n-butyl ether (Dowanol PnB, (Dow Chemicals)), Proglyde® DMM (Dow Chemicals), methoxypropyl acetate and dibasic esters.

The uretdione group-containing curing agents (A11) are free of compounds that are ionically or nonionically hydrophilizing. Compounds that are ionically hydrophilizing are understood by those skilled in the art as meaning compounds having at least one group that is capable of forming anions or cations. Groups capable of forming anions or cations are those that can be converted into an anionic or cationic group through chemical reaction, in particular through neutralization.

The uretdione group-containing curing agents (A11) are preferably free of carboxyl group-containing polyols or diols capable of anion formation, for example dihydroxycarboxylic acids such as α,α-dialkylolalkanoic acids, in particular α,α-dimethylolalkanoic acids such as 2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, or polyhydroxy acids such as gluconic acid. In addition, the uretdione group-containing curing agents (A11) are preferably free of compounds containing amino groups and capable of anion formation such as α,Ω-diaminovaleric acid, 2,4-diaminotoluenesulfonic acid, and the like. The uretdione group-containing curing agents (A11) are likewise preferably free of sulfonic acid groups capable of anion formation.

The uretdione group-containing curing agents (A11) are additionally preferably free of compounds capable of cation formation from the group consisting of tertiary amino or ammonium compounds such as tris(hydroxyalkyl)amines, N,N′-bis(hydroxyalkyl)alkylamines, N-hydroxyalkyldialkylamines, trisaminoalkylamines, N,N′-bis(aminoalkyl)alkylamines, aminoalkyldialkylamines, and mixtures thereof.

The uretdione group-containing curing agents (A11) are further preferably free of nonionic ally hydrophilizing compounds such as polyalkylene oxide polyether alcohols or polyalkylene oxide polyether amines. In particular, the uretdione group-containing curing agents (A11) are preferably free of polyethylene oxide polyethers or mixed polyalkylene oxide polyethers in which 30 mol % or more of the alkylene oxide units consist of ethylene oxide units.

Preferred uretdione group-containing curing agents (A11) have a free NCO content of less than 5% by weight and a content of uretdione groups of 1 to 18% by weight (calculated as C₂N₂O₂, molecular weight 84 g/mol). Apart from the uretdione groups, the curing agents (A11) may also contain isocyanurate, biuret, allophanate, urethane, and/or urea structures.

Suitable polyols (B12) may be selected from polyester polyols, polyether polyols, polyurethane ether polyols, polyurethane ester polyols, polycaprolactone polyols, polyether ester polyols, polycarbonate polyols, poly(meth)acrylate polyols, C2-10 hydrocarbon containing at least two hydroxy groups or mixtures thereof, provided such polyols have at least one chemically bonded carboxylic acid group.

Suitable starting components for the polyols (B12) having at least one chemically bonded carboxylic acid group are polyols, preferably diols, containing at least one carboxylic acid group, generally 1 to 3 carboxylic acid groups per molecule. Examples include dihydroxycarboxylic acids such as α,α-dialkylolalkanoic acids, in particular α,α-dimethylolalkanoic acids such as 2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, and also polyhydroxy acids such as gluconic acid, or aminocarboxylic acids such as α,Ω-diaminovaleric acid, 2,4-diaminotoluenesulfonic acid and the like. Mixtures of the compounds described above may also be used.

Particular preference is given to 2,2-dimethylolpropionic acid as the starting component for the polyols (B12) having at least one chemically bonded carboxylic acid group. Monohydroxy-functional compounds bearing at least one carboxylic acid group, such as hydroxypivalic acid or hydroxydecanoic acid, may also be used less preferably.

Suitable polyols (B12) selected from poly(meth)acrylate polyols are copolymers that contain monomer units bearing carboxylic acid or carboxylic anhydride groups, such as acrylic acid, methacrylic acid, β-carboxyethyl acrylate, crotonic acid, fumaric acid, maleic acid/anhydride, itaconic acid or monoalkyl esters of dibasic acids or anhydrides, such as monoalkyl maleates. Preference is given to acrylic acid or methacrylic acid copolymers.

Suitable polyols (B12) are polyols having an OH content greater than 1% by weight (calculated as OH groups based on the solids content, molecular weight 17 g/mol) and having a number-average molecular weight Mn of 500 to 20 000 g/mol, preferably of 500 to 10 000 g/mol, more preferably of 500 to 5000 g/mol.

The polyurethane resin used according to the invention is preferably produced in such a way that a non-aqueous resin precursor of the polyol (B12) is mixed homogeneously with at least one uretdione group-containing curing agent (A11) based on aliphatic, (cyclo)aliphatic, araliphatic and/or aromatic polyisocyanates, which contains no chemically bound hydrophilizing groups in a non-aqueous system. After this, the carboxylic acid groups present in the polyol (B12) are neutralized with suitable neutralizing agents (N) preferably to an extent of at least 50%, more preferably 80% to 120%, particularly preferably 95 to 105%, and then dispersed with deionized water. The neutralization can take place before, during or after the dispersion step. Neutralization before the addition of water is, however, preferred.

Examples of suitable neutralizing agents (N) are triethylamine, dimethylaminoethanol, dimethylcyclohexylamine, triethanolamine, methyldiethanolamine, diisopropanolamine, ethyldiisopropylamine, diisopropylcyclohexylamine, N-methylmorpholine, 2-amino-2-methyl-1-propanol, ammonia or other customary neutralizing agents or neutralizing mixtures thereof.

Preference is given to tertiary amines such as triethylamine and diisopropylhexylamine, and particular preference to dimethylethanolamine.

Suitable solvents under (C13) are all liquid substances that do not react with other ingredients. Preference is given to acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, Solvesso 100, Solvesso 150, propylene glycol mono-n-butyl ether (Dowanol PnB), methoxypropyl acetate, and dibasic esters. The solvent used may then optionally be removed by distillation.

In accordance with the invention, additives (D14) that are customary in paints and adhesives technology, such as leveling agents such as polysilicones or acrylates, light stabilizers such as sterically hindered amines, or other auxiliaries such those described in EP 0 669 353, may be present in a total amount of 0.05 to 5% by weight. Fillers and pigments such as titanium dioxide may be added to the uretdione dispersion in an amount of up to 50% by weight.

EXAMPLES Methods and Materials: Methods:

Unless stated otherwise, all analytical methods relate to measurements at temperatures of 23° C.

Pendulum Hardness:

Pendulum hardness was measured on a glass plate in accordance with DIN EN ISO 1522:2007-04 and is determined by the Konig method.

Resistance to Solvents and Water:

The resistance of the cured paints to xylene, 1-methoxy-2-propyl acetate, ethyl acetate, acetone, and water was tested. A piece of absorbent cotton soaked in the test substance was laid on the coating surface and covered with a watch glass. After the specified exposure time, the cotton was removed and the exposed area was dried and examined immediately. The softening or discoloration of the coating surface was evaluated in accordance with DIN EN ISO 4628-1:2016-07.

-   0 unchanged, i.e. no noticeable change -   1 very slight, i.e. only visible change, for example minor change in     hue -   2 detectable, i.e. clearly perceptible change, for example softening     discernible by fingernail -   3 clearly noticeable change, for example moderate change in hue,     possible slight blistering -   4 major change, for example severe blistering -   5 coating completely destroyed without any external contact

IR Measurement:

The opening of the uretdione ring was characterized by a Bruker FT-IR spectrometer (Tensor II with platinum ATR module (diamond crystal)). The spectra were recorded in a wavenumber range of 4000-400 cm′. The maximum of the uretdione peak (about 1760 cm′) was evaluated. Peak heights relative to comparison systems were compared at a baseline value set at 100% (uretdione film without catalyst, dried at room temperature). The uretdione peak height of the films cured for 30 min at 180° C. was set at 0%. Variations were determined relative to these 100 and 0% values (ratio calculation).

For measurements on an ATR crystal, the intensity of the spectrum depends on the coverage of the crystal surface. Since it is not possible for the sample preparation to ensure comparable coverage of the crystal surface for comparable measurements, it is necessary for the ratio calculation to correct for this effect by normalizing all spectra to the peak for the CH stretching vibration (wavenumber range) (3000-2800 cm′). The evaluation of the peak heights as described above includes an additional basic correction of the spectra.

The solids content (non-volatile content) was determined by heating a weighed sample to constant weight at 125° C. On reaching constant weight, the solids content is calculated by reweighing the sample.

The NCO content was determined volumetrically in accordance with DIN-EN ISO 11909. The check for free NCO groups was carried out by IR spectroscopy (band at 2260 cm′).

The reported viscosities were determined by rotary viscometry in accordance with DIN 53019:2016-10 at 23° C. using a rotary viscometer at a shear rate of 40 1/s, Anton Paar Germany GmbH, Ostfildern, Germany.

The mean particle sizes (the number average is reported) of the polyurethane dispersions were determined by laser correlation spectroscopy (instrument: Malvern Zetasizer 1000, Malvern Inst. Limited, London, UK) after diluting with deionized water.

The zeta potential was measured by diluting a drop of the sample with 20 ml of demineralized water and homogenizing by stirring. The zeta potential was then determined in the Malvern Nanosizer ZS90 (Malvern Instruments, Herrenberg, Germany) at 23° C.

The acid value of the particular dispersion was determined in accordance with DIN EN ISO 2114: 2002-06. Instead of a mixture of toluene and ethanol as described in DIN EN ISO 2114: 2002-06, the solvent used was a mixture of acetone and ethanol (2:1 by weight). The units for the acid number are mg KOH per g of the analyzed sample.

Materials:

Lupragen N 700 (1,8-diazabicyclo[5.4.0]undecene-7 (DBU)): from BASF SE Sodium 1,2,4-triazolate: from Sigma Aldrich Heloxy modifier TP: polyfunctional glycidyl ether of trimethylolpropane, from Hexion Bayhydrol A2695: water-dilutable, OH-functional polyacrylate dispersion; approx. 41% in water/1-butoxy-2-propanol, neutralized with triethanolamine/dimethylethanolamine, 7.2% 1-butoxy-2-propanol, from Covestro Dowanol PnB: propylene glycol mono-n-butyl ether, from Dow Peroxan DB: di-tert-butyl peroxide: from Pergan Solvent Naphtha 100: an aromatic solvent, from Azelis Butylglycol: from Brenntag Dimethylolpropionic acid (DMPA): from Perstorp Addocat SO: tin(II) 2-ethylhexanoate, from Rhein Chemie, All acrylate monomers and amines (from Sigma-Aldrich) were used as supplied. Veova 9: Versatic acid vinyl ester, from Momentive Other solvents and chemicals: Sigma-Aldrich Xylene (Xy); 1-methoxy-2-propyl acetate (MPA); ethyl acetate (EA); acetone (Ac)

POLYMER SYNTHESIS EXAMPLES Preparation Example 1 Preparation of a Uretdione Polyisocyanate Based on Isophorone Diisocyanate

To 1000 g (4.50 mol) of isophorone diisocyanate (IPDI) were successively added at room temperature under dry nitrogen, and with stirring, 10 g (1%) of triisodecyl phosphite and 20 g (2%) of 4-dimethylaminopyridine (DMAP) as catalyst. After 20 h, the reaction mixture, which had an NCO content of 28.7%, corresponding to a degree of oligomerization of 21.8%, was freed of volatiles, without prior addition of a catalyst poison, with the aid of a thin-film evaporator at a temperature of 160° C. and a pressure of 0.3 mbar.

This yielded a bright yellow uretdione polyisocyanate having a free NCO group content of 17.0%, a monomeric IPDI content of 0.4%, and a viscosity (in accordance with DIN EN ISO 3219:1994-10) of more than 200 000 mPas (23° C.).

Preparation of a Water-Emulsifiable Uretdione Group-Containing Crosslinker

247 g (1.00 equiv.) of the above-described uretdione group-containing polyisocyanate, based on IPDI and having a free isocyanate group content of 17.0% and a calculated uretdione group content of 20.8%, was introduced into 370.3 g of 1-methoxy-2-propyl acetate, mixed with 0.2 g of dibutyltin dilaurate (DBTL) as catalyst, and heated to 80° C. under dry nitrogen. A mixture of 40.6 g (0.90 equiv.) of 1,4-butanediol and 82.5 g (0.11 equiv.) of methoxypolyethylene glycol 750 was then added over a period of 30 minutes and the mixture was stirred at a reaction temperature of max. 105° C. until the NCO content of the reaction mixture had fallen to below 0.1% after about 6 h

-   -   This resulted in a pale yellow solution of a uretdione         group-containing crosslinker having the following properties:         NCO content: <0.1%         Content of uretdione groups (calc.): 6.9%

Monomeric IPDI: 0.09%

Solids content: 50%

Preparation Example 1a

337 g of 1,4-butanediol, 108 of 2-ethylhexanol, and 569 of e-caprolactone were mixed at room temperature under dry nitrogen, 0.3 g of tin(II) octoate was added, and the mixture was stirred at 160° C. for 5 h and then cooled to room temperature. To this mixture was then added, over a period of 30 min, 1850 g of the polyisocyanate from preparation example 1 warmed to 80° C., which was based on IPDI and had a free isocyanate group content of 17.0% and a calculated uretdione group content of 20.8%. The reaction mixture was stirred at a temperature of max. 100° C. until the NCO content of the reaction mixture had fallen to a value of 0.8% after 7 to 8 h. 1910 g of Dowanol PnB was then added to the reaction mixture and the solution was cooled to room temperature.

Preparation Example 2 Preparation of an Anionic Uretdione Prepolymer Dispersion:

218.5 g of IPDI dimer from preparation example 1 was dissolved in 850 g of acetone at 50° C. in a standard stirring apparatus. 22.9 g of dimethylolpropionic acid, 265.9 g of an OH-functional polyester based on 3039 g of adipic acid, 4041 g of isophthalic acid, 267 g of 1,2-propylene glycol, 4773 g of neopentyl glycol, and 1419 g of trimethylolpropane (OH value of the polyester: 181 mg KOH/g) and 0.63 g of tin neodecanoate were added and the mixture was stirred under reflux at atmospheric pressure until the NCO content had fallen to below 0.5%. This was followed by the addition of 16.8 g of N,N-dimethylaminoethanol and 927 g of water. The acetone was removed by distillation under reduced pressure and the viscosity adjusted by adding water.

The resulting white dispersion had the following properties: Solids content: 37.6% Mean particle size: 91 nm Viscosity: 31 mPas Acid value: 7.3 mg KOH/g (based on the dispersion) Zeta potential: 49.6 mV

Preparation Examples 3a-d Preparation Example 3a

TABLE 1 Weight (g) Component 1 DOWANOL PnB 1567 Component 2 PEROXAN DB 33 DOWANOL PnB 33 Component 3 METHYL METHACRYLATE 1243 HYDROXYETHYL METHACRYLATE 2419 n-BUTYL METHACRYLATE 592 n-BUTYL ACRYLATE 723 ISOBORNYL METHACRYLATE 1701 BUTANEDIOL MONOACRYLATE 836 STYRENE 573 Component 4 PEROXAN DB 140 DOWANOL PnB 140 Component 5 BUTANEDIOL MONOACRYLATE 296 METHYL METHACRYLATE 449 HYDROXYETHYL METHACRYLATE 467 n-BUTYL ACRYLATE 379 ACRYLIC ACID 316 Component 6 PEROXAN DB 33 DOWANOL PnB 60 Total amount 12000

Component 1 from table 1 was weighed into a stirring apparatus under nitrogen and heated to 138° C. Component 2 was then metered in uniformly at 138° C. over a period of 20 minutes. After this, component 3 and component 4 were immediately metered in uniformly at 138° C. in parallel over a period of 4 h 30 min. At the end of the addition, the reaction mixture was held at 138° C. for 30 min. Finally, component 5 and component 6 were metered in uniformly at 138° C. in parallel over a period of 1 h 30 min. At the end of the addition, the reaction mixture was held at 138° C. for a further 1 h. The reaction mixture was cooled to 100° C. and then transferred. A slightly yellowish, highly viscous polyacrylate solution was obtained.

500 g of this solution was weighed into a stirring apparatus under nitrogen and heated to 70° C. After homogenizing, 567 g of the solution from preparation example 1a was added and the mixture was homogenized again at 70° C. for 30 min, followed by addition of a mixture of 21.5 g of triethanolamine and 4.3 g of dimethylethanolamine. The mixture was stirred at 70° C. for a further 30 min and then 463 g of distilled water was stirred in to the mixture. Fine adjustment of the viscosity to approx. 2000 mPas afforded a dispersion having the following properties:

Solids content: 43.7% by weight Acid value (100%): 13 mg KOH/g OH content (100%, calculated): 2.8% by weight Mean particle size: 230 nm Viscosity: 2030 mPas

Preparation Example 3b

500 g of polyacrylate solution from preparation example 1 was weighed into a stirring apparatus under nitrogen and heated to 70° C. After homogenizing, 283 g of the solution from preparation example 1a was added and the mixture was homogenized again at 70° C. for 30 min, followed by addition of a mixture of 21.5 g of triethanolamine and 4.3 g of dimethylethanolamine. The mixture was stirred at 70° C. for a further 30 min and then 407 g of distilled water was stirred in. Fine adjustment of the viscosity to approx. 2000 mPas afforded a dispersion having the following properties:

Solids content: 41.7% by weight Acid value (100%): 16.6 mg KOH/g OH content (100%, calculated): 3.6% by weight Mean particle size: 175 nm Viscosity: 2360 mPas

Preparation Example 3c

TABLE 2 Weight (g) Component 1 SOLVENT NAPHTHA 100 900 BUTYLGLYCOL 648 Component 2 PEROXAN DB 33 BUTYLGLYCOL 33 Component 3 METHYL METHACRYLATE 3669 HYDROXYETHYL METHACRYLATE 1816 n-BUTYL ACRYLATE 2603 Component 4 PEROXAN DB 139 BUTYLGLYCOL 139 Component 5 METHYL METHACRYLATE 520 HYDROXYETHYL METHACRYLATE 734 n-BUTYL ACRYLATE 408 ACRYLIC ACID 245 Component 6 PEROXAN DB 33 BUTYLGLYCOL 80 Total amount 12000

Component 1 from table 2 was weighed into a stirring apparatus under nitrogen and heated to 138° C. Component 2 was then metered in uniformly at 138° C. over a period of 20 minutes. After this, component 3 and component 4 were immediately metered in uniformly at 138° C. in parallel over a period of 4 h 30 min. At the end of the addition, the reaction mixture was held at 138° C. for 30 min. Finally, component 5 and component 6 were metered in uniformly at 138° C. in parallel over a period of 1 h 30 min. At the end of the addition, the reaction mixture was held at 138° C. for a further 1 h. The reaction mixture was cooled to 110° C. and then transferred. A pale yellowish, highly viscous polyacrylate solution was obtained.

552 g of this solution was weighed into a stirring apparatus under nitrogen and heated to 70° C. After homogenizing, 471 g of the solution from preparation example 1a was added and the mixture was homogenized again at 70° C. for 30 min, followed by addition of 14.6 g of dimethylethanolamine. The mixture was stirred at 70° C. for a further 30 min and then 466 g of distilled water was stirred in. Fine adjustment of the viscosity to approx. 2000 mPas afforded a dispersion having the following properties:

Solids content: 46.1% by weight Acid value (100%): 16.3 mg KOH/g OH content (100%, calculated): 2.1% by weight Mean particle size: 225 nm Viscosity: 1110 mPas

Preparation Example 3d

TABLE 3 Weight (g) Component 1 DOWANOL PnB 3438 Component 2 PEROXAN DB 33 DOWANOL PnB 33 Component 3 STYRENE 570 METHYL METHACRYLATE 1566 HYDROXYETHYL METHACRYLATE 1601 n-BUTYL ACRYLATE 341 ISOBORNYL METHACRYLATE 1520 n-BUTYL METHACRYLATE 1208 VEOVA 9 1251 Component 4 PEROXAN DB 118 DOWANOL PnB 321 Total amount 12000

Component 1 from table 3 was weighed into a stirring apparatus under nitrogen and heated to 148° C. Component 2 was then metered in uniformly at 128° C. over a period of 20 minutes. After this, component 3 and component 4 were immediately metered in uniformly at 148° C. in parallel over a period of 6 h. At the end of the addition, the reaction mixture was held at 148° C. for 60 min. At the end of the addition, the reaction mixture was held at 148° C. for a further 1 h. The polyacrylate solution was cooled to 80° C. and then transferred.

TABLE 4 Raw material Weights Component 1 Polyacrylate solution from table 3 1993 Component 2 PEROXAN DB 36 DOWANOL PnB 36 72 Component 3 2 - ETHYLHEXYL ACRYLATE 377 HYDROXYETHYL ACRYLATE 1931 n-BUTYL METHACRYLATE 1308 ISOBORNYL METHACRYLATE 2951 n-BUTYL ACRYLATE 338 BUTANEDIOL MONOACRYLATE 555 Component 4 PEROXAN DB 129 DOWANOL PnB 154 Component 5 METHYL METHACRYLATE 533 HYDROXYETHYL ACRYLATE 799 n-BUTYL ACRYLATE 411 METHACRYLIC ACID 333 Component 6 PEROXAN DB 36 DOWANOL PnB 80 Total amount 12000

Component 1 from table 4 was weighed into a stirring apparatus under nitrogen and heated to 144° C. Component 2 was then metered in uniformly at 144° C. over a period of 20 minutes. After this, component 3 and component 4 were immediately metered in uniformly at 144° C. in parallel over a period of 4 h 30 min. At the end of the addition, the reaction mixture was held at 144° C. for 5 min. Finally, component 5 and component 6 were metered in uniformly at 144° C. in parallel over a period of 1 h 30 min. At the end of the addition, the reaction mixture was held at 144° C. for a further 1 h. The reaction mixture was cooled to 100° C. and then transferred. A pale yellowish, highly viscous polyacrylate solution was obtained.

304 g of this solution was weighed into a stirring apparatus under nitrogen and heated to 70° C. After homogenizing, 385 g of the solution from preparation example 1a was added and the mixture was homogenized again at 70° C. for 30 min, followed by addition of 11 g of dimethylethanolamine. The mixture was stirred at 70° C. for a further 30 min and then 324 g of distilled water was stirred into the mixture. Fine adjustment of the viscosity to approx. 2000 mPas afforded a dispersion having the following properties:

Solids content: 42.6% by weight Acid value (100%): 18 mg KOH/g OH content (100%, calculated): 2.5% by weight Mean particle size: 287 nm Viscosity: 2030 mPas

Paint Tests:

Paint Tests on Example Dispersion 1 from Preparation Example 1:

Clearcoats were produced from the following composition:

The uretdione dispersion from preparation example 1 was dispersed in water and then mixed with Bayhydrol A2695 in a SpeedMixer (2000 rpm). Heloxy modifier TP was added, followed by addition of sodium 1,2,4-triazolate (10% in water) and DBU (10% in water, freshly mixed). The mixture was mixed again with a SpeedMixer (2000 rpm) and left to stand on the laboratory benchtop for 30 min to reduce frothing.

The mixture was applied to a glass plate or standardized coil test plate (coil coating black—CS 200570, from Heinz Zanders Prüf-Blech-Logistik) in a layer thickness of 150-180 μm (wet) using a coating bar. The plates were dried at room temperature for 5 minutes and then oven baked at 100° C. for 30 minutes. The performance of the resulting films was evaluated and an IR spectrum was recorded.

Example 4: Formulations and Comparative Formulations Using Example Dispersion 1

SC (%) C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 11 Bayhydrol A 42.90 20.0 20 20.0 20.0 20.0 20.0 20.0 20.0 20.0 20.0 2695 Dispersion 50.00 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 28.5 preparation example 1 in MPA Demineralized 10 34.4 34.4 34.4 34.4 34.4 34.4 34.4 34.4 34.4 water Heloxy 100.00 0.49 0.49 0.49 0.49 0.49 modifier TP 1,2,4- 10.00 2.30 2.30 2.30 2.30 Triazole-Na in water Lupragen 10.00 2.30 2.30 2.30 2.30 N700 (DBU) in water C = comparative example, non-inventive SC = solids content in % Performance Tests/Physical Properties of the Paints from Example 4:

C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 11 Ring — — >97 >97 >97 >97 >97 12 >94 94 <4 opening¹ König 98 110 128 170 189 181 156 198 181 171 195 pendulum hardness (sec) Resistances² 0-5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 1/1/2/2 3/3/4/5 3/3/3/3 0/0/0/1 Resistances³ 0-5 4-5 4-5 4 4 4 4 4 4 4 4 1-2 C = comparative example, non-inventive Curing conditions unless explicitly stated otherwise are 30 min at 100° C. ¹ = IR intensity of uretdione peak having peak max. between 1750 and 1800 cm⁻¹ in % ² = versus Xy/MPA/EA/Ac, applied to sheet metal for 5 minutes ³ = versus water, applied to glass for 1 hour

Paint Tests on Example Dispersion 2:

Clearcoats were produced from the following composition:

Heloxy modifier TP, sodium 1,2,4-triazolate (10% in water), and DBU (10% in water, freshly mixed) were added to the uretdione dispersion from preparation example 2 and the resulting mixture was mixed in a SpeedMixer (2000 rpm) and then left to stand for 30 min to reduce frothing.

The mixture was applied to a glass or sheet metal in a layer thickness of 150-180 μm (wet) using a coating bar. The plates were dried at room temperature for 5 minutes and then oven baked at 100° C. for 30 minutes. The performance of the resulting paints was evaluated and an IR spectrum was recorded.

Example 5: Comparative Tests and Tests with Formulations Using Example Dispersion 2

SC C1 C2 C3 C4 C5 C6 7 Dispersion from 31.00% 20.00 20.00 20.00 20.00 20.00 20.00 20.00 preparation example 2 Triazole-Na in 10.00% 1.20 1.20 1.20 water DBU in water 10.00% 0.62 0.62 0.62 0.62 Heloxy modifier TP 0.38 0.38 0.38 C = comparative example, non-inventive SC = solids content (%) Performance Tests/Physical Properties of the Paint from Example 5:

C1 C2 C3 C4 C5 C6 7 Ring opening¹ >97 >97 >97 87 80 31 <3 König pendulum 216 215 217 198 213 220 226 hardness (sec) Resistances² 0-5 5/5/5/5 5/5/5/5 5/5/5/5 3/3/4/4 5/5/5/5 1-2/3/3-4 1/1/2/4 Resistances³ 0-5 0 1-2 1 1 1 0 0 C = comparative example, non-inventive Curing conditions unless explicitly stated otherwise are 30 min at 100° C. ¹ = IR intensity of uretdione peak having peak max. between 1750 and 1800 cm⁻¹ in % ² = versus Xy/MPA/EA/Ac, applied to sheet metal for 5 minutes ³ = versus water, applied to glass for 1 hour Paint Tests on Dispersions from Preparation Examples 3a-d:

Clearcoats were produced from the following composition:

The uretdione dispersion from preparation examples 3a-d was in a SpeedMixer (2000 rpm) with the uretdione dispersion from preparation example 1, Heloxy modifier TP, sodium 1,2,4-triazolate (10% in water) and DBU (10% in water, freshly mixed). The mixture was left to stand for 30 min to reduce frothing.

The mixture was applied to a glass or sheet metal in a layer thickness of 150-180 μm (wet) using a coating bar. The plates were dried at room temperature for 5 minutes and then oven baked at 100° C. for 30 minutes. The performance of the resulting coatings was evaluated and an IR spectrum was recorded.

Example 6: Comparative Tests and Tests with Formulations from Preparation Examples 3a-d

SC C1 C2 C3 C4 C5 C6 C7 C8 9 10 11 12 13 14 15 16 3a 41.7% 10.0 30.0 20.0 30.0 3b 43.7% 10.0 30.0 20.0 30.0 3c 46.1% 10.0 30.0 20.0 30.0 3d 42.6% 10.0 30.0 20.0 30.0 1 50.0% 31.3 25.5 20.2 22.2 31.3 25.5 20.2 22.2 Demineralized 36.0 32.0 25.0 30.0 2.0 2.0 2.00 2.00 34.00 33.00 28.00 29.00 water Heloxy 100.0%  0.36 0.30 0.39 0.40 0.54 0.45 0.59 0.60 modifier TP 1,2,4- 10.0% 0.83 0.87 0.92 0.85 2.80 2.60 2.30 2.50 Triazole-Na in water Lupragen 10.0% 0.83 0.87 0.92 0.85 2.80 2.60 2.30 2.50 N700 (DBU) in water Crosslinking 0.22 0.44 0.5 0.5 1.0 1.0 1.0 1.0 0.22 0.44 0.5 0.5 1.0 1.0 1.0 1.0 ratio C = comparative examples SC = solids content (%) Performance Tests/Physical Properties of the Paints from Example 6:

C1 C2 C3 C4 C5 C6 C7 C8 Ring opening¹ >97 >97 >97 >97 >97 >97 >97 93 König pendulum 61 93 55 80 131 152 114 129 hardness (sec) Resistances² 0-5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 5/5/5/5 Resistances³ 0-5 4 4 3 3 2 2 1 1 C = comparative example, non-inventive Curing conditions unless explicitly stated otherwise are 30 min at 100° C. ¹ = IR intensity of uretdione peak having peak max. between 1750 and 1800 cm⁻¹ in % ² = versus Xy/MPA/EA/Ac, applied to sheet metal for 5 minutes ³ = versus water, applied to glass for 1 hour

9 10 11 12 13 14 15 16 Ring opening¹ <3 <3 <3 <3 <3 <3 <3 <3 König pendulum 126 97 115 155 167 194 189 189 hardness (sec) Resistances² 0-5 3/4/4/5 2/3/3/4 2/4/4/4 3/4/4/4 1/1/1/1 0/0/1/1 0/1/1/4 0/0/2/4 Resistances³ 0-5 3-4 4 2 2 1 1-2 1-2 1 C = comparative example, non-inventive Curing conditions unless explicitly stated otherwise are 30 min at 100° C. ¹ = IR intensity of uretdione peak having peak max. between 1750 and 1800 cm⁻¹ in % ² = versus Xy/MPA/EA/Ac, applied to sheet metal for 5 minutes ³ = versus water, applied to glass for 1 hour

The curing reaction can be monitored by monitoring the opening of the uretdione ring by IR spectroscopy. With the combination of sodium triazolate, DBU and Heloxy modifier TP, the IR peak for uretdione has almost disappeared (<4% based on the height of the uretdione peak of the dried starting material). The pendulum hardness also increases with the efficacy of the catalyst mixture. Resistance to xylene, MPA, EA, and acetone needs to be at least 1/1/2/4; water resistance must be at least 1-2. Both resistances can be achieved only through the catalyst mixture. In example 6 it can be seen that an equimolar amount of uretdione to alcohol (entries 13 to 16) results in much higher hardness values and better resistances than an excess of alcohol (entries 9 to 12). 

1: A catalyst system comprising A) at least one compound selected from the group consisting of azoles, oxazoles, thiazoles, benzotriazole, benzimidazole, benzoxazole, and salts thereof; B) at least one acid scavenger containing at least one epoxy group; and C) at least one catalyst containing an N,N,N′-trisubstituted amidine structure and having an amidine group content of 12.0 to 47.0% by weight calculated as CN2 with molecular weight=40. 2: The catalyst system as claimed in claim 1, wherein the at least one compound A) is selected from pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, benzotriazole, and salts thereof. 3: The catalyst system as claimed in claim 1, wherein the at least one acid scavenger B) is selected from aliphatic or aromatic alcohols, diols, polyols, ethers and acids containing at least one epoxy group. 4: The catalyst system as claimed in claim 1, wherein the at least one catalyst containing an N,N,N′-trisubstituted amidine structure and having an amidine group content of 12.0 to 47.0% by weight calculated as CN2, molecular weight=40, C) is selected from optionally substituted amidine bases bearing alkyl, aralkyl or allyl radicals, wherein the CN double bond of the amidine structure is both part of an open-chain molecule and an element of a cyclic or bicyclic system, or else may be positioned exocyclically on a ring system, or any desired mixtures of such amidines. 5: The catalyst system as claimed in claim 1, wherein A) and B) are present in a mass ratio of 1:1 to 10:1 and/or A) and C) are present in a mass ratio of 0.5:1 to 5:1 and/or B) and C) are present in a mass ratio of 1:1 to 1:10. 6: A kit comprising the catalyst system as claimed in claim 1 and an aqueous uretdione dispersion wherein the dispersion has an acid value of 1 to 100 mg KOH/g and at least one carboxyl group. 7: The kit as claimed in claim 6, wherein the equivalents ratio of uretdione to hydroxy groups is 0.5:1 to 1:0.5. 8: A process for producing a polyurethane layer comprising the steps of i) providing an aqueous uretdione dispersion having an acid value of 1 to 100 mg KOH/g and having at least one carboxyl group; ii) adding the catalyst system as claimed in claim 1 to produce a mixture; iii) applying the mixture obtained in ii to a substrate); iv) drying the mixture from step iii), and v) curing the mixture from step iv) by heating to 120° C. for up to 180 minutes. 9: A polyurethane layer, obtained by the process as claimed in claim
 8. 10: In a process for curing aqueous uretdione dispersions having an acid value of 1 to 100 mg KOH/g and having at least one carboxyl group, or for producing paints or coatings the improvement comprising including the catalyst system as claimed in claim
 1. 